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field of view, angles, size of 35mm negative - Photography

I need to know the angle subtended by an object that is on a 35mm negative. It was taken with a 38mm lens and the focus was at infinity. It is 2.7mm wide on the negative. Here are my rough calculations. Can someone verify them or correct them? My calculations: I calculate that a 38mm lens has a field of view of approximately 59 degrees (please check this). If a 35mm negative is 24x36mm (or is it a little larger?), the diagonal is 43.27mm. 43.27mm on the negative corresponds to 59 degrees in the field of view, so each mm ...

  1. #1

    Default field of view, angles, size of 35mm negative

    I need to know the angle subtended by an object that is on a 35mm
    negative. It was taken with a 38mm lens and the focus was at
    infinity. It is 2.7mm wide on the negative.

    Here are my rough calculations. Can someone verify them or correct
    them?

    My calculations:

    I calculate that a 38mm lens has a field of view of approximately 59
    degrees (please check this).

    If a 35mm negative is 24x36mm (or is it a little larger?), the
    diagonal is 43.27mm. 43.27mm on the negative corresponds to 59
    degrees in the field of view, so each mm on the negative corresponds
    to 1.3635 degrees in the field of view. So 2.7mm of the object on the
    negative corresponds to subtending approximately 3.68 degrees (round
    it off to 3.7).

    Are these calculations right, or can they be improved?

    TIA.
    Jud Guest

  2. #2

    Default Re: field of view, angles, size of 35mm negative

    Not sure about the field of view/diagonal assumption.
    For obvious reasons, 35mm film usually has two field of view (FOV) angular
    dimensions; horizontal and vertical.

    F.O.V. = 2 * arctan(Film Dimension/(2 * Focal Length))
    (assuming magnification is zero)

    I think you need to factor in the X,Y offset between your two points of
    measurement.

    HTH

    "Jud McCranie" <net> wrote in message
    news:com... 


    Mr3 Guest

  3. #3

    Default Re: field of view, angles, size of 35mm negative

    On Mon, 3 Nov 2003 10:40:06 -0800, "Mr3"
    <&#106;&#104;&#097;&#114;&#114;&#105;&#115;&#051;& #064;&#115;&#112;&#101;&#097;&#107;&#101;&#097;&#1 15;&#121;&#046;&#110;&#101;&#116;>
    wrote:
     

    This gives a different formula for fisheye lenses, but that doesn't
    seem to agree with regular lenses
    http://www.vrphotography.com/data/pages/askexperts/pano/fovfisheye.html

    It also gives the 35mm frame size as 24.3x35.8 mm (instead of 24x36).

    Your formula gives 1.51 degrees/mm instead of the 1.38 I roughly
    calculated.

    I found this website, and it gives
    http://www.reftools.com/reftools/Arts/Photography/Photography.html
    gives 50.7 degrees H, 35.05 degrees V, 59.3 degrees diagonal.

    That corresponds to 1.46 degrees /mm in the vertical direction, 1.41
    in horizontal, and 1.37 diagonal.

    I don't know why they would be different, unless the angle subtended
    is not the same at the center of th frame compared to the edges, but
    that is true, isn't it?

    Jud Guest

  4. #4

    Default Re: field of view, angles, size of 35mm negative

    Just the facts...
    38mm lens - most manufacturers round off the numbers for marketing purposes.
    Let's assume that the lens is within 1 or 2 mm which puts all calculations
    at plus or minus 5%.

    Frame size - the film starts out blank. The camera exposes a frame based on
    the physical attributes of the 'hole' behind the shutter. Everything I read
    says this hole should be sized to produce a 24 x 36mm exposed area. I think
    the alternate size of 24.3 x 35.8mm is for projection film frames which
    loose width to optically encoded sound tracks and gain height due to smaller
    intra-frame spaces. For your purposes, can you measure your negative?

    Formulas - the common formulas assume a 'standard' lens with no distortion.
    This excludes fisheyes and zoom lenses at their extremes which produce
    barrel and pincushion distortion.

    Angular measurements - 35mm frames are asymmetrical for your purposes. The
    formula results are only good for calculating dimensions in the dimensional
    direction used in the formula. If you use 24mm (vertical film dimension) in
    the formula, the results can only be applied to objects in the frame that
    are exactly vertical. Ditto Horz and Diag. Imagine a picture of a 24"h x
    36"w rectangle in the center of the frame. If you use the horizontal frame
    dimension in the formula, and apply the result to the vertical measurement,
    the resulting angular calculations would make the rectangle into to a
    square.

    Hope that makes sense.

    Mr3


    "Jud McCranie" <net> wrote in message
    news:com... 
    <&#106;&#104;&#097;&#114;&#114;&#105;&#115;&#051;& #064;&#115;&#112;&#101;&#0
    97;&#107;&#101;&#097;&#115;&#121;&#046;&#110;&#101 ;&#116;> [/ref]
    angular 
    >
    > This gives a different formula for fisheye lenses, but that doesn't
    > seem to agree with regular lenses
    > http://www.vrphotography.com/data/pages/askexperts/pano/fovfisheye.html
    >
    > It also gives the 35mm frame size as 24.3x35.8 mm (instead of 24x36).
    >
    > Your formula gives 1.51 degrees/mm instead of the 1.38 I roughly
    > calculated.
    >
    > I found this website, and it gives
    > http://www.reftools.com/reftools/Arts/Photography/Photography.html
    > gives 50.7 degrees H, 35.05 degrees V, 59.3 degrees diagonal.
    >
    > That corresponds to 1.46 degrees /mm in the vertical direction, 1.41
    > in horizontal, and 1.37 diagonal.
    >
    > I don't know why they would be different, unless the angle subtended
    > is not the same at the center of th frame compared to the edges, but
    > that is true, isn't it?
    >[/ref]


    Mr3 Guest

  5. #5

    Default Re: field of view, angles, size of 35mm negative

    On Mon, 3 Nov 2003 20:23:05 -0800, "Mr3"
    <&#106;&#104;&#097;&#114;&#114;&#105;&#115;&#051;& #064;&#115;&#112;&#101;&#097;&#107;&#101;&#097;&#1 15;&#121;&#046;&#110;&#101;&#116;>
    wrote:
     

    I just measured one from my camera, which is not the one that took the
    photo in question. To the best that I can read the ruler, it is
    precisely 24x36mm. I'll have to get my hands on the actual negative
    again to check it, maybe tomorrow.
     

    Yes, I thought the formula for fisheye lenses that I found seemed way
    off.

    Thanks, again.

    Jud Guest

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